1. Field of the Invention
The present invention relates to a light emitting diode and a fabricating method thereof. More particularly, the present invention relates to a light emitting diode with high light-emitting efficiency and a fabricating method thereof.
2. Description of the Related Art
A light emitting diode (LED) is a semiconductor device fabricated using a group III-V compound semiconductor material, for example. The semiconductor material has a special property capable of converting the electrical energy into optical energy. More specifically, the electrons and holes within the semiconductor material will recombine to release the excessive energy in the form of light when a current is sent through the semiconductor material. Hence, the LED is able to emit light.
Because the light produced by the light emitting diode is a type of cold emission but not thermal emission nor electric discharge, the working life of a light emitting diode device often exceeds a hundred thousand hours. Furthermore, light emitting diodes do not require idling time. In addition, light emitting diode devices have a very high responsive speed (about 10−9 seconds), a very low degree of pollution (no mercury contained) and very high reliability. Moreover, they are of a very small volume, use very little electricity and are particularly suitable for mass production. With these advantages, the applications of light emitting diodes are far and wide.
In general, a light emitting diode mainly comprises a substrate, a semiconductor layer and a plurality of electrodes. The semiconductor layer is a composite stack comprising a P-type doped layer, an active layer and an N-type doped layer. The semiconductor layer is disposed on the substrate and the electrodes are disposed on the semiconductor layer. When an electric potential is formed between the N-type doped layer and the P-type doped layer, electrons and holes will recombine together in the active layer to produce light.
The light emitting efficiency of the aforesaid light emitting diode depends mainly on the quantum efficiency of the light emitting layer and the light extraction efficiency of the entire light emitting diode. The quantum efficiency of the light emitting layer mainly depends on the epitaxy quality and structure of the light emitting layer and the light extraction efficiency mainly depends on the effective utilization of the light produced by the light-emitting layer (active layer).
To enhance the light extraction efficiency of the light-emitting diode, one conventional technique is to roughen the surface of the light-emitting diode. This technique is typically performed in the post-end production process of the light-emitting diode. The process includes roughening the surface of the light-emitting diode to prevent the occurrence of total internal reflection of light inside the light-emitting diode to reduce the overall light utilization. Because this technique requires an additional roughening process in the fabrication of the light-emitting diode, a higher production cost is incurred and longer production period is required.
In addition, the conventional technique also includes forming a metallic reflective layer between the semiconductor layer and a passivation layer to increase the light extraction efficiency of the light-emitting diode. However, this method still requires the fabrication of an additional metallic reflective layer and hence incurring additional production cost.